She hit upon the idea of starting a do-it-yourself dog wash while standing in her shower one day, shampooing her own two pets. Now, celebrating its 20th year, Jane Donley’s Ocean Beach business is doing — pardon the pun — doggone well.

Last month, a 7½-pound pug became her 450,000th “customer,” said Donley, who owns Dog Beach Dog Wash on Voltaire Street with her partner, Mindy Pellissier.

Donley said between 400 and 500 dogs a week are bathed in the shop’s five waist-high tubs and a puppy sink, mostly after a romp on nearby Dog Beach. The doors are open from 7 a.m. to 9 p.m., seven days a week.

“Our biggest day was in August 2004, when we had 168 dogs in 14 hours,” Donley said. “Our biggest week was in 1999 with 716 dogs … I believe this makes us the busiest dog wash in the country.”

To mark the occasion, Oscar the pug and his “guardians,” Carolyn and Rob Voss, got a free wash and a gift bag of coupons, doggie toys and treats. And at 8:20 a.m., when the dog ambled in, there were mimosas for all the adults.

Donley recalls when her late dog Breaker, an Australian-shepherd mix, had a flea allergy and needed to be bathed every day for two weeks. Living in a condo, she said, she didn’t have a yard and had to do the honors in her shower.

Then, the dogs ran through the house shaking off water. Cleaning the dogs, the house and all the towels, took about four hours.

“And I never thought the dogs got cleaned very well,” Donley said.

So, with the new business idea in mind, she walked to Dog Beach to run her idea by other pet owners. They loved it and promised to use the shop that would be just a few blocks from the popular beach. “Everyone said they had planned to open one, and we did it.”

In less than two years, Donley, a former public relations manager in the health field, and her partner, a former nurse, were turning a profit. Not a huge one, but a profit, Donley said. The income pays the bills. “And I finally paid off the bank this year.”

When they opened, they charged $5 for owners to wash their own dogs. Two decades later, the dog wash is offering the do-it-yourself shampoos with 90-degree water for $13, a little extra for specialty shampoos and cream rinses. Plastic aprons — an obvious necessity — are available for free. There’s a professional on hand for nail trimming at $13.

Akira, a lab and basenji mix loves the place, according to owner Amy Ouska, who recently swung by on the way home from Dog Beach.

“It’s so much easier here,” said Ousaka. “You can stand and don’t have to bend over.”

Donley didn’t build walls between the sinks because, she believes, the dogs like to socialize with each other.

Unlike when the dogs visit their veterinarians, there’s no stress here, Donley said.

“We try to make it fun and light-hearted,” she said.

And even the dogs who are a little skittish get free treats on the way out.

The best part of the dog wash, Oscar’s “parents” told Donley, “The dogs and people are happy when they come and even happier when they leave.”

Friendly dogs and their owners are invited to join Friends of Dog Beach for beach cleanups from 9 to 11 a.m. on the second Saturday of each month. Gloves, bags, scoops, brooms and shovels are provided. For more information, call (619) 523-1700.